Greenhouses typically have one or more transparent walls and roofs that allow solar radiation to penetrate into the structure for plant photosynthesis. It is difficult to control the growing conditions within a greenhouse without expending significant energy. Many greenhouses now in operation are open greenhouses. This is required because ventilation is needed on hot days to remove heat from the greenhouse.
For example, greenhouses have a tendency to accumulate large quantities of heat in their interiors when the sun is shining brightly. For certain plant species, this extra heat has to be removed to keep a favourable temperature for plant growth. This is normally done by venting the heat from within the greenhouse. In hot and humid conditions, one or more fans are used, which consumes energy, and are prone to mechanical failure. This climate control requiring that the greenhouse be open to the atmosphere reduces the ability to control the greenhouse's humidity and CO2 levels, and exposes the plants to insects, bacteria or other airborne contaminants in polluted regions. Such open greenhouses also have a tendency to leak heat to the atmosphere during cool nights or during the winter season in northern-latitude regions, which inhibits plant growth.
Most greenhouses have only one level of plants, often near the ground level of the installations. This requires a relatively large footprint to install such greenhouses in order to achieve the desired production capacity. Other methods use complicated mechanisms to move plants around to better expose the plants to natural or artificial light or to minimize labour. These mechanisms are often difficult to implement and are subject to failures during the lifespan of the greenhouse.